Food color chemistry Flashcards
Describe Chlorophyll
Chlorophyll is a pigment found in green plants that help plants carry out photosynthesis.
Its chemistry can be altered by high heat or pH changes.
There are chlorophyll a and chlorophyll b
Describe the formation of pheophytin
As green vegetables are heated and parts of their cell membranes are disrupted, some organic acids are released and reacts with chlorophyll, forming pheophytin, an unattractive olive-green pigment. The magnesium atom in chlorophyll is replaced by a hydrogen atom to form pheophytin. This reactions occur faster in acidic solution as opposed to neutral solution.
Describe the formation of chlorophyllin
Heating green vegetables in alkaline solutions, produces chlorophyllin, a bright green semi-synthetic mixture of water-soluble sodium copper salts derived from chlorophyll that can dye things into a delightful range of soft greens, from forest green to sea green.
Explain the process whereby vegetables get softer over heat
The texture change is due to significant amounts of hemicellulose in the vegetables cells being partially dissolved when heated in hot water.
Hemicellulose is responsible for cell wall strength and when significant amount of hemicellulose is lost from the vegetable cells to the heated water solution, the vegetable texture goes from hard to soft because the cell walls are weakened.
Hemicellulose is solubilized more quickly in heated alkaline solution, thus heating vegetables in alkaline solution quickly results in very soft textures
What did we do in this practical?
We separated peas into 4 beakers, being control, heated, 0.01N HCl and 0.01N NaOH. We heated 20g each of peas and heated them in these 4 solutions for
20 minutes. We then isolated the peas and record the color and texture.
There is dull olive green color and bright green color.
There is no change in texture, softer than original and softest amongst all variables.
